Blending devices are well known to those skilled in the art. Thus, for example, U.S. Pat. No. 4,813,787 of Conn discloses a blending apparatus containing a rotating disc, or discs, comprising two features: (a) holes in the disc with louvers of various size and shape to transport material axially through the disc for improved blending, and (b) tangentially arranged teeth at the perimeter of the disc, bent up and down at various angles to the plane of the disc to serve as "masticaters."
U.S. Pat. No. 3,630,636 of Hill discloses a mixing apparatus comprised of two rotating discs, each of which include oppositely disposed slot deflectors arranged in two concentric circular arrays to transport material through the holes in opposing directions. These discs have no teeth on their perimeters.
U.S. Pat. No. 3,222,038 of Ashcraft discloses a mixing machine comprised of three discs, the top and bottom rotating counterclockwise and the middle disc rotating clockwise. Vanes above the top disc and below the bottom disc feed the material from above and below the stack of three discs, through concentrically located holes in each disc, into the middle disc, thus maximizing mixing, dispersion, or comminution.
U.S. Pat. No. 3,030,083 of Stiffler discloses an agitator wheel comprised of two rotating discs, both of which have radial slots and concentric rows of holes. The purpose of the slots is to allow the leading edge of the slot to be bent upward and the trailing edge of the slot to be bent downward, or the reverse, to impart an axial flow of the viscous material. Each disc has its slot edges bent in the opposite direction relative to the other one in order to force the viscous material against itself between the two discs thus maximizing shear forces.
U.S. Pat. No. 2,871,000 of Dowling discloses a glass stirring device which contains a plurality of discs on a single shaft each containing holes which are not in registry with those in an adjoining disc. The discs are joined together with radially mounted webs between them. These webs also have non registering holes in them to force a molten glass to the perimeter of the vessel and into intimate contact with the glass at the perimeter. The non registry of the holes in both discs and webs is designed to maximize the tortuosity of the flow path the glass must traverse thereby maximizing mixing efficiency.
U.S. Pat. No. 2,598,469 of Korshenewsky discloses a rotor for homogenizers with various shaped grooves on its surface only.
U.S. Pat. No. 2,268,038 of Knittel discloses a mixing machine which contains a depressed center disc rotor mounted at the bottom of a tank. The disc has agitator louvers extending radially and upwardly from the upper surface of the rim. Beneath these louvers are holes connecting the top and bottom of the disc. Beneath the outer rim are angled impeller vanes. Within the depressed center are agitator vanes.
The disclosure of each of the aforementioned patents is hereby incorporated by reference into this specifications. The discs used in the devices of these patents comprise unprotected protrusions above and/or below the disc(s) and holes through the discs. None of these patents have addressed the problem of severe wear due to abrasion by large particles, or the energy necessary to effectively deagglomerate fine powders; and none of these patents has provided a solution to this problem.
The Shar Mixer Company of Fort Wayne, Texas, for example, produces a mixer which uses an agitator disc with flame-sprayed tungsten carbide coatings on its steel teeth. Although this agitator is somewhat more durable than a similar agitator which uses uncoated steel teeth, it still has a relatively short life when used with crowded hard particulate suspension systems.
It is an object of this invention to provide an apparatus for the high shear mixing and deagglomeration of fine powders in crowded suspensions which is substantially more durable and effective than prior art devices.